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If it's bad we say so
Page 67
Page 68
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... or how CM tests its vehicles
by Graham Montgomerie
ONE of the major functions of Commercial Motor is to appraise commercial vehicles — especially new ones and those destined for the British market -in order to provide operators and engineers with unbiased and comparative assessments of performance and suitability.
To judge from readers' reactions, and the number of requests for reprints we receive, our test reports are widely read here and overseas. But the published reports are only the tip of the iceberg — a condensed representation of perhaps three days of hard testing. We are often asked to explain how this or that figure is arrived at; and in the belief that a knowledge of what goes on behind the scenes can provide a useful insight into the scope and accuracy of our written reports, this article records what happens on a typical heavy-vehicle road test and operational trial.
CM's tests are not all of the same type; as readers will know, we test vehicles ranging from three-wheeled vans to 40tonne artics over a variety of routes, and our bus and coach tests are a different matter again. But the three-day test of a heavy road-going artic is probably the most demanding example of our work, so it's the one I've chosen to describe here.
On the road
•
The CM heavy-vehicle road test and operational trial lasts three days and is divided into two sections; a 1,173 km (729-mile) road route from Hertfordshire to Scotland and back, covering all types of road in two days; and a day of performance testing at the Motor Industry Research Association's roving ground, where we investigate he aspects of performance which annot easily or safely be tested on ublic roads.
The road section of the CM test nvolves a drive from Hemel Hempstead o the Stair Arms at Pathhead near dinburgh, and back to Hemel by a ifferent route. This circuit was devised ome years ago by the CM technical taff and it incorporates a wide variety • f road classifications. The out-and-out • logging ability of the motor can be tested on the longer motorway gradients such as Keele and Charnock Richard and the ride and handling performance can be assessed on the winding roads south out of Scotland through Carter Bar and Rochester.
Carter Bar on the Scotland/ England border is one of several severe winding hills on the route and we put the stop watch on the vehicle at this point for the 2.9 km (I .8-mile) climb which can usually be relied upon to spotlight any deficiencies in power output or transmission matching. Times for this test, using 32-tonners as examples, range from just under five minutes for the more powerful units to around eight minutes.
Although we stick to main roads; the section from Carter Bar, through West Woodburn and Ridsdale is really punishing and sorts out the performers with something in hand from those designed for a softer life.
Fuel economy
Fuel economy has become even more important to the operator in recent months and on our tests we keep a careful log of fuel consumption. With the variety of roads and the length of the test, the fuel figures we achieve are representative of typical haulage use, although I think we seldom reach the figures hoped for by the manufacturers! Our fuel stops are arranged to divide the route into motorway, normal A roads and the really stiff sections — so it is possible to see from our Operational Trial results table how the fuel consumption varies with the different conditions.
Each day on the road averages around 10 hours driving, and at the end of a day, any shortcomings in the cab have usually made themselves evident. Any driver will know that a unit which is comfortable at the start of a shift may be the opposite when he finishes. By the time we reach Pathhead at the end of the first day we are in a position to comment on the good or bad points of the cab design, especially those concerning the seating position and control layout.
We can now enlist the aid of the Department of the Environment as witnesses to the fact that CM staff really do spend hours at the wheel: on a recent road test of the first "British" Saviem 32-240, we were stopped by traffic examiners for a logbook check two miles south of Scotch Corner. Being, of course, legal on every count we were allowed to proceed!
From the road route we obtain a detailed log of time, distance and fuel used — the raw material for our published average speed and fuel consumption figures.
Testing at MIRA
Some of the testing we obviously cannot do on public roads — one cannot make full-pressure stops from 40 mph in the middle of Al, Apart from this obvious example, the facilities at MIRA enable us to evaluate the hill-restarting capabilities of the unit in question and to measure the vehicle's acceleration on the measured mile. MIRA also has a useful ride and handling course.
The hill restart test is one of the simpler tasks, thanks to the provision at the testing grounds of accurate test hills. Various gradients from I in 6 to 1 in 3 are available and we simply drive the truck up the 1 in 6 slope, stop, apply the handbrake and then restart. At least that is what should happen in practice, other things have been known to occur, such as propshafts w[nding up and breaking.
If the vehicle completes the restart satisfactorily the next steepest gradient is attempted, and so on until the limit of the vehicle's ability is arrived at or all the hills are climbed. The latter stage is not reached very often, as very few vehicles can manage a hill start from rest, fully laden, on a 1 in 3 gradient. On the test hills we also try the parking brake's holding ability.
The gradeability of a vehicle is a somewhat nebulous quality. On some of our road tests a truck has stormed up the worst section (1 in 6) of our road route at Ridsdale in fine style but has ground to an ignominious, clutch-slipping halt on MIRA's 1 in 6 — indicating the tremendous difference that a rolling. start can make.
Brake tests
We can measure the efficiency of a iehicle's regular braking systems in two vays: by chalk gun or Motometer. In nactice we usually use both methods to )rovide a cross-check on the accuracy of he results.
The chalk-gun is simplicity itself. A nessure pad fixed to the brake pedal :ompletes an electrical circuit when the 'ootbrake is applied, and this instananeously fires a chalk pellet at the ground under the foremost point of the rehicle. The distance from the chalk nark to where the front of the vehicle Inally comes to rest can then be neasured. These tests are carried out 'rom 32, 48 and 64 km/ h (20, 30 and tO mph) and, knowing the initial vehicle ;peed, the final speed (ie zero) and the ;topping distance, the retardation can 3e calculated in terms of "g" or !.xpressed on a percentage basis.
The alternative method is to use a Motometer which has the added advantages of measuring the pedal !ffort required to achieve a certain -etardation as well as recording the .nformation on a chart for a permanent record. The Motometer recording unit .s placed on a suitable level surface in the ab (many engine cowls are useful for this purpose) and the pressure pad mounted on the brake pedal in a similar manner to the brake gun. On applying the brakes the Motometer measures the deceleration and pedal effort, while two itylii inside the unit record the infOrmation on a chart which is pumped out at one end. The only disadvantage of the Motometer is that it requires a second person to operate, whereas the chalk gun can be operated by the driver alone.
For measuring the retardation produced by the trailer brake and the handbrake we use a Tapley meter. This consists of a rotating drum in a housing which is clamped to the vehicle as close as possible to its overall centre of gravity. When the vehicle stops, the drum does not and the amount it rotates provides the measurement of the braking effect. The Tapley meter can also be used in conjunction with the chalk gun to measure the maximum (or peak) deceleration, as opposed to the average deceleration. For example, in stopping from 40 mph a vehicle can record an overall deceleration of 0.5g, while a maximum of 0.7g occurs at one point during the stop.
Vehicle performance
Acceleration from rest, fully laden, is another test made easy at MIRA by the provision of the two dead-level parallel straights. At times MIRA can seem one of the windiest places on earth and the reason for having two straights is to enable the average performance to be measured, thus eliminating this wind effect. With trucks fitted with boxvan bodies or container-carrying trailers this difference can be remarkable. In a recent road test of a Ford D0707 fitted with a boxvan body, the acceleration times from 0 to 40mph varied from 40 seconds to 55 seconds depending on the direction of the runs. The times are measured using a split-action stopwatch which allows several times to be recorded on the same run. The two acceleration straights are joined at each end by a steeply banked portion so that the vehicle speed can be maintained through a 180° change in direction. Negotiating the banking at about 50 km/h (37 mph) can be quite an experience in a fully laden 32-tonner!
Measurements
Most manufacturers provide us with dimensional chassis drawings as the basis for the diagrams published with our test reports but, especially with ail:4es, we have to take many of our own measurements. It is necessary to run a tape-measure over the overall length of a vehicle to see whether it conforms with C and U Regulations. It has been known for a test vehicle to be supplied to us with axle spreads which are less than the legally required dimension and also, in the case of artics, over the 15 m limit. In cases like this we have to ask the manufacturer to swop it for a legal outfit — otherwise, no test.
Visibility from the driving seat can be assessed by marking the point on the ground where an object becomes hidden from the driver by the base of the windscreen and measuring the distance along the projected centreline of the cab.
As well as driving the vehicles over a long route to assess their characteristics from what is principally a driver's viewpoint, and measuring the performance and economy in a way which is mainly of interest to the owner or transport manager, we take a look at some of the features which will help to decide a fitter's or workshop foreman's temper. How accessible are the regularly serviced items? Are vulnerable items exposed to road filth or weather? Would we fancy changing an injector or topping up with oil on a wet night?
Evaluating the results
From the sheaves of paper covered with comments and figures collected over three days we marshal orderly opinions and tabulated results. From our staff photographer's large batch of pictures taken on the test we select the ones we feel will give the most realistic impression of the vehicle and its attributes and shortcomings. (The first time the manufacturer sees the test report is when he reads it in CM, like everyone else.) Testing vehicles can be very enjoyable, but it is also hard work and sometimes — with a poor performer — exceedingly wearing. We nevertheless try to find the good and the bad points in each test vehicle, and assess the machine according to its type and quality. I think our reports are as near as one can get to providing an unbiased appraisal for the operator; obviously no necessarily brief test is going to show how a vehicle will stand up to haulage operation involv ing perhaps 200,000 miles a year but sometimes we can provide a clue.
Within these limitations, I hope CM's road test reports satisfy a need on the part of the operator — and he's the man they're written for.